The Oceans Are Going to Rise—but When?

The archetypal version of this story appeared in Quanta Magazine.

In May 2014, NASA announced astatine a property league that a information of the West Antarctic Ice Sheet appeared to person reached a constituent of irreversible retreat. Glaciers flowing toward the oversea astatine the periphery of the 2-kilometer-thick expanse of crystal were losing crystal faster than snowfall could replenish them, causing their edges to recede inland. With that, the question was nary longer whether the West Antarctic Ice Sheet would disappear, but when. When those glaciers go, oversea levels volition emergence by much than a meter, inundating onshore presently inhabited by 230 cardinal people. And that would beryllium conscionable the archetypal enactment earlier the illness of the full crystal sheet, which could rise seas 5 meters and redraw the world’s coastlines.

At the time, scientists assumed that the nonaccomplishment of those glaciers would unfold implicit centuries. But successful 2016, a bombshell survey successful Nature concluded that crumbling crystal cliffs could trigger a runaway process of retreat, dramatically hastening the timeline. The Intergovernmental Panel connected Climate Change (IPCC) took notice, establishing a sobering caller worst-case scenario: By 2100, meltwater from Antarctica, Greenland, and upland glaciers combined with the thermal enlargement of seawater could rise planetary oversea levels by implicit 2 meters. And that would lone beryllium the beginning. If greenhouse state emissions proceed unabated, seas would emergence a staggering 15 meters by 2300.

However, not each scientists are convinced by the runaway scenario. Thus, a hostility has emerged implicit however agelong we person until West Antarctica’s immense glaciers vanish. If their retreat unfolds implicit centuries, humanity whitethorn person clip to adapt. But if accelerated destabilization begins successful the coming decades done the arguable runaway process, the consequences could outpace our quality to respond. Scientists pass that large colonisation centers—New York City, New Orleans, Miami and Houston—may not beryllium ready.

“We’ve decidedly not ruled this out,” said Karen Alley, a glaciologist astatine the University of Manitoba whose probe supports the anticipation of the runaway process. “But I’m not acceptable to accidental it’s going to hap soon. I’m besides not going to accidental it can’t happen, either.”

For millennia, humanity has flourished on the shore, unaware that we were surviving successful a geological fluke—an antithetic spell of debased seas. The oceans volition return, but however soon? What does the subject accidental astir however crystal sheets retreat, and therefore, astir the aboriginal of our ports, our homes, and the billions who unrecorded adjacent the coast?

Grounded by the Sea

In 1978, John Mercer, an eccentric glaciologist astatine Ohio State University who allegedly conducted fieldwork nude, was among the archetypal to foretell that planetary warming threatened the West Antarctic Ice Sheet. He based his mentation connected the crystal sheet’s uniquely precarious narration with the sea.

Bigger than Alaska and Texas combined, West Antarctica is divided from the eastbound fractional of the continent by the Transantarctic Mountains, whose peaks are buried to their chins successful ice. Unlike successful East Antarctica (and Greenland), wherever astir crystal rests connected onshore precocious supra the water, successful West Antarctica the crystal expanse has settled into a bowl-shaped slump heavy beneath oversea level, with seawater lapping astatine its edges. This makes West Antarctica’s crystal expanse the astir susceptible to collapse.

A heaping dome of ice, the crystal expanse flows outward nether its ain value done tentacle-like glaciers. But the glaciers don’t halt astatine the shoreline; instead, colossal floating plates of crystal hundreds of meters heavy widen implicit the sea. These “ice shelves” interval similar elephantine rafts, tethered by resistance forces and interaction with underwater rises and ridges. They buttress the glaciers against an inexorable gravitational gully toward the sea.